Patent GB-549928-A (GB)
Title: Improvements in and relating to web registering mechanisms
IPC: B65H23/04
Filed: 1941-03-10
Abstract: 549,928. Feeding webs. AMERICAN MACHINE & FOUNDRY CO. March 10, 1941. No. 3235. Convention date, April 25, 1940. [Class 100 (i)] To ensure register of printed matter on a web of wrapping or other material with a cutting or other apparatus, the web feeding roller is stopped when spaced marks on the web having different dielectric capacity or conductivity from the web arrive at a position between two detector members in a high frequency oscillating circuit, the capacity effect between the mark and the detecting members causing a current impulse which is caused to supply a current to an electro magnet and thereby open a clutch in the drive to the web feeding roller. As shown, two detector plates A, B are arranged adjacent to the path of the web W in a high frequency oscillating circuit including a transformer T 2  and oscillator valve V4 and primary Pi of a transformer T<SP>1</SP>. The arrival of a mark M opposite to the plates A, B causes a change in the capacity of the circuit giving rise to a current which is detected by a valve V1. Part of the voltage generated by the valve V4 passes to a resistance R8 and a rectifying valve V<SP>5</SP> and the resulting direct current voltage across a pair of potentiometers R<SP>9</SP>, R<SP>10</SP> is tapped and applied as negative bias, almost to current cut-off, to the grids of a pair of valves V<SP>1</SP>, V<SP>2</SP>. The filaments of the valves V<SP>1</SP>, V2, V 4  and V<SP>5</SP> are heated by current furnished by a secondary S3<SP>111</SP> of a transformer T3 supplied from the mains L. Another secondary S3<SP>11</SP> of this transformer is connected at its mid point through a choke T4 and resistance R<SP>7</SP> to a resistance R<SP>4</SP> in the plate circuit of the valve V <SP>1</SP> and also through a resistance R3 to the primary of the transformer S2. Between the choke and resistan ce R7 a connection is taken through a condenser C<SP>12</SP> to the plate of valve V<SP>2</SP> and the opposite sides of the condenser are connected, one side through a switch Sw<SP>2</SP>, to an electromagnet E serving to disconnect a clutch K in the drive to the web-feed roller F.A third secondary S3 of the transformer T3 is connected at mid-point to earth and at its ends to the plates of a rectifying valve V3 the filament of which is heated by the secondary S3<SP>11</SP>. The current impulse applied to the transformer T by the arrival of a mark M at the detecting point causes a direc current voltage to be applied across a resistance R<SP>2</SP> in the cathode circuit of the valve V<SP>1</SP> which voltage is applied, through the potentiometer G<SP>1</SP> and resistance R<SP>5</SP> to the grid of valve V<SP>2</SP>. This valve is a gaseous valve and the potential applied to its grid ionises the gas rendering the valve conductive so that current flows from the valve V3 through the switch Sw2, magnet E and valve V<SP>2</SP> so that the clutch K is opened. At a subsequent period in a cycle of operations, the switch Sw is opened by a cam X to break the circuit of the magnet E and de-ionize the valve V2. The clutch is then closed by a spring H. In a modification, Fig. 6, the marks M on the web pass between the primary and secondary coils P, S of a transformer T, these coils being arranged respectively in the plate circuit and grid-filament circuit of an oscillator V, the current impulst due to the arrival of a mark actuating a relay Re to operate the magnet E. The detector plates may be arranged side by side longitudinally of the web as shown, side by side laterally of the web, or one on each side of the web. An earthed plate may be arranged between the plates to increase their sensitivity.